I thought it would be a good idea to post this here as a warning to anyone that's thinking of buying a USB-GDROM. I've long suspected this was a thing but didn't have solid proof until now. Mnemo has implemented what is essentially self-destructing firmware into his USB-GDROM devices. After a certain amount of time, the device will stop working (you'll get a "Firmware Obsolete" message when trying to run a game) and require you to update the firmware. This is a security measure he implemented to prevent cloning. A very bad one though. If he ever disappears and doesn't release periodic firmware updates, USB-GDROMs will start dropping like flies.
There's a thread on Twitter
talking about this right now which contains confirmation from Mnemo himself that this is true. I should note that this seems to have been implemented in a later firmware update so if you're still on an old one, it's best not to update. Mnemo claims he will release an update to remove this "firmware expiry" but we'll see. In the meantime, it's probably best to avoid buying one.